After surgery, illness, pregnancy or extended inactivity for any reason, people might feel faint or fatigued when they try even mild exercise. These signs, Joyner argues, should be recognized by doctors not as symptoms that should be treated with drugs, but rather as a medical state of deconditioning that might be better helped with a gentle, guided exercise program.

It might sound counterintuitive that fatigue can be beat back with exercise. But remember Newton—Isaac, not Fig. A body at rest stays at rest. And a body in motion needs to resist external forces acting upon it that might slow it down.